deviantart: fix page_url for when api data is unavailable.

The api data is unavailable when we can't scrape the uuid, either
because the work is deleted or because the work is actually a sta.sh
upload and we weren't given the sta.sh page in the referer url.

app/logical/sources/strategies/deviant_art.rb

@@ -87,8 +87,13 @@ module Sources
       end
 
       def page_url
-        return "" if api_deviation.blank?
-        api_deviation[:url]
+        if api_deviation.present?
+          api_deviation[:url]
+        elsif api_url.present?
+          api_url
+        else
+          ""
+        end
       end
 
       def profile_url